Andy are you suggesting the capacitive dropper+ the opto?
The opto provides isolation, so the schematic from pokemon has isolation.

About using it without cross detection, you could modulate power by turning on for a number of cycles, then off for a number of cycles, rather than for a percentage of each cycle.

In that way you may turn on in the middle of a cycle, which is not ideal, but then you stay for for say the period of 200 cycles, and then off for 55 (if you use 8bits of resolution).
You could then set the timer to match your mains frequency (50 or 60 hz), but you will not be in sync. I think that would cause more interference to other systems.

I wanted to know if there was an opportunity, run on two timers, that's all.

You can, the switching won't be synchronized with the AC wave, so no good for lighting, but for a heater you should be ok.
I do something similar for my reflow oven controller, and works fine, though I plan to enable zerocross detection now that I have a custom board for it.

Because the response time of a heater is so slow, you probably don’t need the zero crossing detector.

but It depends on the purpose of the system.

I built a system to use surplus solar electricity, and it was very important that the system did not use more power in each cycle ( actually each half cycle) than was available in the surplus

So tuning in a 4kW heater for 1 second and then off for 9 seconds to give 10% power usage was no good, because for those 9 seconds all the surplus power goes to waste, and in the first 1 second, the system needs to get 3.6kW from the grid.

Andy: I saw and example circuit that used a capacitor instead of resistors , but I am not sure how well it works.

There is even an Atmel application note where they connect the MCU GPIO directly to the mains via a very high value resistor.

I.e. It is possible to power the MCU via one of those capacitive power supplies , so that the whole circuit is not isolated from the mains, and you don’t need an opto at all, as you can drive the gate of the triad directly from the MCU ( assuming the MCU can deliver enough current from its GPIO, e.g. via paralleling a whole port of pins together and turning them all on or off at the same time using the BSSR reg)

And if control is via radio, the whole thing can be safely put in an isolated box.

However... it’s very hard to debug problems in this scenario, and if you get things wrong the MCU goes up in smoke very quickly

So it’s not an approach I have taken. But it is the approach used by those radio controlled inline mains sockets

For power I use a switching power supply, everything is in a plastic box and only the encoder has a metal handle
I also met the circuit where a diode bridge and a mosfet are used, but I have never tried it

Last edited by pokemon99 on Mon Dec 11, 2017 8:22 pm, edited 1 time in total.